"Reverse a given cashback," like cashback granting, only accepts the cancellation request.
Since the cancellation process is executed asynchronously, even if the response is SUCCESS, the granted Cashback may not have been completed canceled.
Be sure to execute the "Check Cashback Reversal Details" API and confirm the status.
Reference specification: https://www.paypay.ne.jp/opa/doc/jp/v1.0/cashback#tag/GrantAndReverseCashback/operation/createCashbackReversal